On 2020/5/25 13:25, Damien Le Moal wrote: > On 2020/05/22 21:19, Coly Li wrote: >> Hi folks, >> >> This is series, now bcache can support zoned device (e.g. host managed >> SMR hard drive) as the backing deice. Currently writeback mode is not >> support yet, which is on the to-do list (requires on-disk super block >> format change). >> >> The first patch makes bcache to export the zoned information to upper >> layer code, for example formatting zonefs on top of the bcache device. >> By default, zone 0 of the zoned device is fully reserved for bcache >> super block, therefore the reported zones number is 1 less than the >> exact zones number of the physical SMR hard drive. >> >> The second patch handles zone management command for bcache. Indeed >> these zone management commands are wrappered as zone management bios. >> For REQ_OP_ZONE_RESET and REQ_OP_ZONE_RESET_ALL zone management bios, >> before forwarding the bio to backing device, all cached data covered >> by the resetting zone(s) must be invalidated to keep data consistency. >> For rested zone management bios just minus the bi_sector by data_offset >> and simply forward to the zoned backing device. >> >> The third patch is to make sure after bcache device starts, the cache >> mode cannot be changed to writeback via sysfs interface. Bcache-tools >> is modified to notice users and convert to writeback mode to the default >> writethrough mode when making a bcache device. >> >> There is one thing not addressed by this series, that is re-write the >> bcache super block after REQ_OP_ZONE_RESET_ALL command. There will be >> quite soon that all seq zones device may appear, but it is OK to make >> bcache support such all seq-zones device a bit later. >> >> Now a bcache device created with a zoned SMR drive can pass these test >> cases, >> - read /sys/block/bcache0/queue/zoned, content is 'host-managed' >> - read /sys/block/bcache0/queue/nr_zones, content is number of zones >> excluding zone 0 of the backing device (reserved for bcache super >> block). >> - read /sys/block/bcache0/queue/chunk_sectors, content is zone size >> in sectors. >> - run 'blkzone report /dev/bcache0', all zones information displayed. >> - run 'blkzone reset -o <zone LBA> -c <zones number> /dev/bcache0', >> conventional zones will reject the command, seqential zones covered >> by the command range will reset its write pointer to start LBA of >> their zones. If <zone LBA> is 0 and <zones number> covers all zones, >> REQ_OP_ZONE_RESET_ALL command will be received and handled by bcache >> device properly. >> - zonefs can be created on top of the bcache device, with/without cache >> device attached. All sequential direct write and random read work well >> and zone reset by 'truncate -s 0 <zone file>' works too. >> - Writeback cache mode does not support yet. >> >> Now all prevous code review comments are addressed by this RFC version. >> Please don't hesitate to offer your opinion on this version. >> >> Thanks in advance for your help. > > Coly, > > One more thing: your patch series lacks support for REQ_OP_ZONE_APPEND. It would > be great to add that. As is, since you do not set the max_zone_append_sectors > queue limit for the bcache device, that command will not be issued by the block > layer. But zonefs (and btrfs) will use zone append in (support for zonefs is > queued already in 5.8, btrfs will come later). Hi Damien, Thank you for the suggestion, I will work on it now and post in next version. > > If bcache writethrough policy results in a data write to be issued to both the > backend device and the cache device, then some special code will be needed: > these 2 BIOs will need to be serialized since the actual write location of a > zone append command is known only on completion of the command. That is, the > zone append BIO needs to be issued to the backend device first, then to the > cache SSD device as a regular write once the zone append completes and its write > location is known. > Copied. It should be OK for bcache. For writethrough mode the data will be inserted into SSD only after bio to the backing storage accomplished. Thank you for all your comments, I start to work on your comments on the series and reply your comments (maybe with more questions) latter. Coly Li
